Numerical modelling of bank erosion in meandering river channels

摘要

Riverbank erosion is an environmental problem with global significance. It is an effective factor in land loss and sediment generation in river channels. Thus, the simulation and prediction of bank erosion, particularly in meandering river channels, are very important. Because of the complexity of the bank erosion process, many existing models cannot completely simulate this process. This is due to the fact that the bank erosion process has three components including fluvial entrainment (erosion by water flow), bank instability (bank collapse under gravity) and sediment transport (removal of failed debris). The majority of existing models can simulate only one and/or two components of the bank erosion process. Moreover, these models do not account for the influence of secondary currents. Due to the importance of secondary current effects on outer bank erosion in meandering river channels, their simulation should be considered. Therefore, in this research, two different numerical models have been employed, namely a three-dimensional flow and sediment transport model (SSIIM-3D, Olsen 2001) and a two-dimensional flow, sediment transport and bank erosion model (RIPA-2D, Darby 2001). As experimental channels are the best tools for the evaluation of numerical models, the first part of this research has been focused on the simulation of flow structures in an experimental meandering channel (Riprap Test Facility, Vicksburg, Mississippi) with the use of SSIIM-3D. In the second stage, the RIPA-2D numerical model has been used to simulate the flow structure and bank erosion pattern in a meandering river channel (Fall River, Rocky Mountain National Park, Colorado). The results obtained show that SSIIM-3D has the capability to simulate accurately velocities, velocity distributions and, particularly, secondary current patterns at different cross sections of Riprap Test Facility. Furthermore, simulations associated with Fall River indicate that RIPA-2D may be applied to predict flow structure and the pattern of bank erosion in natural rivers.